CN1131983A

CN1131983A - Screened capacitive sensor

Info

Publication number: CN1131983A
Application number: CN94193515.9A
Authority: CN
Inventors: 罗格·L·弗里克
Original assignee: Rosemount Inc
Current assignee: Rosemount Inc
Priority date: 1993-09-24
Filing date: 1994-08-15
Publication date: 1996-09-25
Also published as: JPH09503294A; EP0740777B1; WO1995008752A2; US5424650A; EP0740777A1; DE69423004D1; DE69423004T2; SG67884A1; WO1995008752A3; RU2144680C1; JP3448060B2; CA2169823A1

Abstract

A pressure sensor(10) measures pressure by measuring capacitance between two capacitive plates(114, 116). Pressure change appears as a change in capacitance. Stray capacitance interferes with this measurement. The stray capacitance arises between the capacitor plates(114, 116) and surrounding material. Circuitry(140) reduces stray capacitance by maintaining substantially no potential difference between a capacitor plate(114, 116) and surrounding material responsible for stray capacitance.

Description

Screened capacitive sensor

The present invention relates to a kind of pressure transducer, relate in particular to a kind of capacitive pressure transducer, it has the circuit that reduces effect of parasitic capacitance.

Prior art has been showed different solid state pressure sensors, and these sensors have a diaphragm that is offset that is used for detected pressures, and some are can be mass-producted.Desirable is to adopt the strong material of relative stiffness, the solid state pressure sensor of doing as semiconductor material.

Capacitance pressure transducer, comes gaging pressure by measuring two electric capacitys between the capacitor plate.Pressure changes the variation that shows as electric capacity.Stray capacitance can be introduced in the capacitance measurement on a pressure transducer made from semiconductor, and causes measuring error.This stray capacitance occur in capacitor plate and near play between the semiconductor material of a capacitor plate effect.

The name that is published on September 16th, 1986 is called the United States Patent (USP) 4,612,599 of " capacitance pressure transducer, ", has showed a kind of pressure transducer made from silicon.The name that is published on January 3rd, 1989 is called the United States Patent (USP) 4,800,758 of " the stress isolation formula sensator that rigidity is installed ", has described a kind of pressure transducer of the stress isolation formula that can make in batch.

The invention provides the circuit that is used for capacitance pressure transducer,, it has reduced the influence that stray capacitance is measured the electric capacity of decision working liquid pressure size.Circuit comprises a transformable detection electric capacity, and this electric capacity has first and second capacitor plates, and the electric capacity between the pole plate is as the function of measured parameter.Every capacitor plate all has corresponding to the stray capacitance that is laid in first and second capacitor plates fender on every side.A reference voltage source is provided, and driving circuit provides the driving voltage of a relative reference current potential alternate for first capacitor plate.The testing circuit that links with reference potential produces a virtual reference potential; it equals reference potential substantially; the charge detection circuit that links with second capacitor plate detects the quantity of electric charge at second capacitor plate; after the electric charge transfer was finished, making between second capacitor plate and the fender did not have potential difference (PD) like this.

Fig. 1 is a fragmentary, perspective view according to floated pressing diaphragm force transducer of the present invention.

Fig. 2 is the cut-open view of Fig. 1 along mark line 2-2.

Fig. 3 is the cut-open view of Fig. 1 along mark line 3-3.

Fig. 4 is a profile perspective according to differential pressure transducer of the present invention.

Fig. 5 is a right cut-open view of diaphragm according to the present invention, shows a group capacitor.

Fig. 6 is the schematic diagram of a protection condenser network.

Fig. 7 is the cut-open view of a differential pressure transducer, and the capacitor plate that is used for gaging pressure is shown.

Fig. 8 is circuit theory diagrams that reduce effect of parasitic capacitance according to the present invention.

Pressure sensor thin slice of the present invention is finished with manufacturing technology in batch. Silicon diaphragm or Silicon sheet is to be etched with common mode to form desired characteristic, and it is suitable to add then The material extra play forms layer structure and becomes sensor. At this as a reference, such sensing Device is applied on September 20th, 1993, and has been transferred the application's same assignee's name Be called in the U.S. Patent application of " floated diaphragm pressure sensing device " and narrated.

The pressure transducer that makes with semiconductor material often produces stray capacitance, and this stray capacitance can cause tonometric error.The generation of electric capacity is because semiconductor is incomplete conductor, and can serve as the pole plate of capacitor, so at the capacitor plate that is used for gaging pressure with stray capacitance just occurs between the semiconductor (fender) on every side.

Fig. 1 is the fragmentary, perspective view of a floated pressing diaphragm force transducer 10.Floated pressing diaphragm force transducer 10 comprises subtegulum 12 and last substrate 14, following diaphragm substrate 16 bonding subtegulum 12, following diaphragm substrate 16 links together with upper diaphragm substrate 18.Following diaphragm substrate 16 has pipeline 20 and electric contact chip 22 and 24, and pressure inlet 26 passes substrate 14 and stretches out, and upper diaphragm substrate 18 comprises the upper diaphragm 28 by back up pad 30 supportings.

Fig. 2 is the cut-open view of Fig. 1 along the floated pressing diaphragm force transducer 10 of mark line 2-2.Fig. 3 is the cut-open view of Fig. 1 along the floated pressing diaphragm force transducer 10 of mark line 3-3.Fig. 2 illustrates down diaphragm 32 with Fig. 3 and is connected upper diaphragm 28, upper diaphragm 28 and following diaphragm 32 have formed a diaphragm unit with film chamber 34, chamber 34 generally has a reference pressure that adds via passage 20, upper and lower diaphragm 28 is in the same place along their edge downlink connection with 32, and upper diaphragm 28 and following diaphragm 32 are suspended in 36 li of pressure input cavities.This input cavity and pressure inlet 26 connect together.

In use, floated pressing diaphragm force transducer is used to pressure differential between test chamber 34 and the chamber 36, expand in pressure input cavity 36 or compress with the variation of response by pressure inlet 26 applied pressures in film chamber 34, this just causes that upper diaphragm 28 and following diaphragm 32 are crooked or outwardly-bent by film chamber 34 in film chamber 34.Liquid flows to chamber 34 or exhaust chamber 34 by pipeline 20, and pipeline 20 passes back up pad 30 and stretches out.

Diaphragm

28 and 32 bending (therefore being applied in pressure) are detected by electric contact chip 22 and 24, these contact chips are coupled to the sensor that is contained on diaphragm 28 and the diaphragm 32, in one embodiment, these sensors are exactly capacitor plate or metallic conductor, diaphragm 28 has a capacitor plate, diaphragm 32 has a capacitor plate, and the electric capacity between these two pole plates is owing to two-plate changes because of producing displacement by 26 applied pressures of pressure inlet.In another embodiment, electric contact chip 22 and 24 is coupled on the foil gauge that is contained on the diaphragm, and the resistance of foil gauge changes along with the distortion of

diaphragm

28 and 32.

In a preferred embodiment, floated pressing diaphragm force transducer 10 is by easily crisp material, forms as monocrystalline silicon or sapphire material, makes in batch.These materials have been owing to reduced hysteresis, and have improved the stability of shape and improved precision.Furtherly, resemble the such material of silicon, pottery and glass, use known manufacturing technology be easy to mass-producted.

Fig. 4 is the profile perspective according to a floated diaphragm differential pressure transducer 40 of the present invention.Sensor 40 is made up of a pair of pressure transducer, and this sensor is similar to pressure transducer shown in Figure 1 10, has a pipeline (Fig. 4 is not shown) that resembles the pipeline 20 of Fig. 1 and stretches between diaphragm unit.

Differential pressure transducer 40 comprises subtegulum 42, last substrate 44, and following diaphragm substrate 46 and upper diaphragm substrate 48 apply differential pressure by pressure inlet 50A and

50B.Pressure inlet

50A and 50B are coupled to

diaphragm unit

54A and 54B respectively, and diaphragm unit 54A comprises upper diaphragm 58A and following diaphragm 60A, shape film forming chamber 62A between the two, and film chamber 62A is arranged in pressure input cavity 64A, and the latter is connected to pressure inlet 50A.The structure of diaphragm unit 54B is identical with diaphragm unit 54A's.

In differential pressure transducer 40, though film chamber 62A is not shown by a Fig. 4, but be similar to the pipeline junctional membrane chamber 62B of the pipeline 20 among Fig. 1, the passage of connection chamber 62A and chamber 62B passes back up pad, and these back up pads are supporting diaphragm unit 54A and the 54B in chamber 64A and the chamber 64B respectively.A certain amount of abrim relative incompressible seal fluid in chamber 62A and the chamber 62B makes that another chamber can be shunk when a chamber expands owing to impressed pressure.

The bending of floated diaphragm and institute's applied pressure among the present invention (or differential pressure, or absolute pressure) relevant.By detecting this distortion, just can determine the size of pressure.Using any suitable means can carry out this detection measures.In a preferred embodiment, detect the distortion of diaphragm, be with a pole plate on each diaphragm by measuring capacitance variations between two pole plates of a capacitor.Fig. 5 is the sectional view of a floated diaphragm 108, it has comprised upper diaphragm 110 and following diaphragm 112, have capacitor plate 114 and following capacitor plate 116 separately respectively,

pole plate

114 and 116 is installed on

diaphragm

110 and 112 by

insulation course

118 and 120 respectively separately, and the space between the

diaphragm

110 and 112 forms the chamber 122 that best notes oil.

Fig. 5 illustrates capacitor C A, and this is the electric capacity between

pole plate

114 and 116, the numerical value of capacitor C A and the pressure correlation that puts on floated diaphragm 108.Therefore, just can determine the pressure size by measuring electric capacity.Yet stray capacitance CS1 and CS2 can influence this measurement.This stray capacitance is by between pole plate 114 and the diaphragm 110, and produce respectively between pole plate 116 and the diaphragm 112 electric capacity caused, this electric capacity be because

insulation course

118 and 120 respectively with

pole plate

114 and 116 and the result that separates of

diaphragm

110 and 112, therefore, need from the measurement of CA, eliminate this stray capacitance.

Fig. 6 shows and simplifies circuit 124, it is used to eliminate the influence to the CA measurement that is caused by CS1 and CS2, circuit 124 comprises that connection capacitor C A is driven the square wave drive device 130 of end, an end (the being substrate 112) electrical grounding of the end of capacitor C S1 (being substrate 110) and CS2, the test lead of capacitor C A is linked the positive input terminal of operational amplifier 132, operational amplifier 132 forms negative feedback loop by integrating capacitor 134, the in-phase input end of operational amplifier 132 provides virtual earth potential, and the capacitance measurement circuit that is used for calculating pressure is supplied with in the output of operational amplifier 132.

Circuit 124 makes substrate 110 and substrate 112 keep same current potential with test pole 116, and this is to make test pole 116 remain on virtual earth potential because have degenerative operational amplifier 132.Test the stray capacitance brought error with regard to having reduced the circuit that is not connected test pole 116 owing to CS2 like this for pressure test.

Fig. 7 is the sectional view of

diaphragm unit

54A and 54B, shows the capacitor plate that is used for gaging pressure.Capacitor plate is linked on A, B, C and the D of terminals, and

diaphragm unit

54A and 54B are received on the electric connection terminal E.

Fig. 8 is a schematic diagram that utilizes the circuit 140 that the present invention reduces effect of parasitic capacitance.Circuit 140 illustrates capacitor C 1 and the C2 that electric capacity changes along with the differential pressure between diaphragm unit 54A and the 54B.That follow capacitor C 1 is capacitor parasitics CS11 and CS12, and that follow capacitor C 2 is capacitor parasitics CS21 and CS22, these electric capacity owing to around semiconductor material cause.Fig. 8 shows electric connection terminal A, B, C, D and the E that also illustrated in Fig. 7.Terminals A and D are connected on together, and this connection can externally or directly be done on pressure transducer 40, with the quantity of the electric connection terminal that reduces pressure transducer 40.

Circuit 140 comprises the operational amplifier 142 that is connected to Schmidt trigger 144, and operational amplifier 142 forms negative feedback loop by integrating capacitor CI, and the output terminal of Schmidt trigger 144 is linked on the DLC (digital logic circuit) 146, power supply+V _RWith-V _RReceived the E utmost point, and receive the A utmost point and the D utmost point respectively through switch SW 6 and SW5, the B utmost point is then received operational amplifier 142 by switch SW 1, and the C utmost point is received operational amplifier 142 by switch SW 4, and the E utmost point is received the in-phase input end of operational amplifier 142.The B utmost point and the C utmost point are linked the E end respectively by switch SW 2 and SW3.Switch SW 1 to SW6 is received the DLC (digital logic circuit) 146 that is used to control these switches.

Be in operation, operational amplifier 142 provide one with capacitor C 1 and C2 between the relevant relevant output of just testing with sensor 40 of differential pressure of the difference of electric capacity.This is a kind of technology of measuring electric capacity, and being called in the name of people such as Jim Furyk application in the U.S. Patent No. 5,083,091 of " charging balance feedback test circuit " has narration.

Operational amplifier 142 remains on the test pole on capacitor C 1 and the C2 on the virtual voltage potential and (remains virtual earth potential in one embodiment).After electric charge is assigned with, do not have electric charge to flow out from CS11, CS12, CS21 or CS22, these electric capacitys just can not enter in the measurement like this.Circuit will use+V _RWith-V _RPower supply drive CS11 and CS22.

Charging current is:

I charging=F excitation * (V _R-(V _R)) * (CS11+CS22)

Use exemplary value, about 0.07 milliampere (CS11 and CS22 are approximately 200 * 10 to this electric current ^-12Farad), because charging current is more much smaller than 4 milliamperes of minimum watt currents, this electric current can coexist with 4-20 milliampere current return.

Finish when charging and to carry out electric capacity when test, circuit keeps the B utmost point to be in the extremely the same current potential with E with the C utmost point, and this is because when finishing when charging, the cause that the output of the integrator of being made up of operational amplifier 142 is sampled at this point.

Though the present invention narrates with reference to preferred embodiment, those skilled in the art will recognize and not deviate from the spirit and scope of the present invention, can make a little changes in form and details, for example when stray capacitance becomes a problem, also can use the present invention by the sensor or the sensor design of other types.

Claims

1. testing circuit comprises:

A variable test capacitors, have first and second capacitor plates, electric capacity between two-plate is as the function of detected parameter, and each capacitor plate all has the stray capacitance corresponding to fender, and these fenders are laid in around first and second capacitor plates;

A reference voltage source;

A driving circuit provides a driving voltage with respect to the reference potential alternate for first capacitor plate;

A testing circuit that is connected to reference potential, and produce a virtual reference current potential that equals reference potential haply;

Be connected to the on-off circuit of second capacitor plate, it alternately is connected to second capacitor board on reference potential and the virtual reference current potential, and making does not have potential difference (PD) basically between second capacitor board and fender.

2. the testing circuit of claim 1, wherein fender is made by semiconductor material.

3. the testing circuit of claim 1, wherein the virtual reference current potential is one and has by the degenerative operational amplifier of integrating condenser.

4. the testing circuit of claim 1, wherein detected parameter is a pressure.

5. a form that is used for pressure function provides the pressure test circuit of pressure test output, and it comprises:

One has one and drives pole plate and a detection electric capacity that detects pole plate, the function as pressure of electric capacity between plate;

One in the stray capacitance that detects between pole plate and the stray capacitance pole plate;

A reference potential that is connected to the stray capacitance pole plate;

The virtual reference which couple is to reference potential, and it has a virtual reference current potential output that equals reference potential haply, and output is relevant with the electric capacity that detects capacitor;

Be connected to the charge detection circuit that detects pole plate, detect at the electric charge that detects on the pole plate, and keep detecting pole plate substantially with the same current potential of stray capacitance pole plate on, therefore, stray capacitance has been eliminated stray capacitance in fact from the test volume of testing capacitor; And

The output circuit of pressure survey output is provided according to detected electric charge.

6. the pressure test circuit of claim 5, wherein the stray capacitance pole plate is made by semiconductor material.

7. the pressure test circuit of claim 5, wherein the virtual reference current potential is one and has by the degenerative operational amplifier of integrating condenser.